Gas turbine rotatable blades of first blade rows of a gas turbine can be designed with a blade shroud at their tips extending circumferentially along a blade row. The blade shroud can limit an amount of working fluid flow leaking through a clearing gap between the blade tips and a flow channel wall and can thereby maximize an effect of the working fluid on the rotatable blades. In first stages of a gas turbine, where temperatures of turbine gases can be at their highest, the rotatable blades can be fully shrouded. The blade shrouds form a continuous ring encompassing the blade tips and an entire circumference of the blade row thereby minimizing the hot gas flow reaching the flow channel walls. A blade shroud can include one or more fins, also known as knife-edges, that extend radially or partially radially away from the shroud and towards a gas turbine stator and flow channel wall.
The stator or inner casing of the turbine forming the flow channel wall includes carriers for vanes as well as thermal heat shields mounted on its inner walls.
The heat shields can protect the wall of the flow channel, or gas turbine inner casing, from the high-temperature gas flow driving the gas turbine and thereby can assure an economical operating lifetime.
The blade shrouds and flow channel wall with heat shields can be actively cooled by cooling flows directed to the shroud and heat shields. EP 1 219 788 for example, discloses a gas turbine with blade shrouds and heat shields that are cooled by a cooling airflow passing through a cooling channel extending through an inner casing and heat shield and leading to a space between two fins of the blade shroud and the heat shield. From that space, the cooling flow passes over the shroud and the fins to both leading and trailing edges of the blade shroud, where it can enter into the hot gas flow of the turbine. The cooling air requires an appropriate pressure level for the cooling flow to reach the leading edge of the shroud by flowing in a direction opposite the direction of the hot gas flow.
EP 2009248 discloses a gas turbine and a cooling arrangement for the cooling of the rotatable blade tips including a cooling flow passage directing a cooling flow to the leading edge of the blade shroud. A leakage flow from the gas turbine flow channel is allowed to reach the exit opening for the cooling passage and mix with the cooling flow emerging from the passage.